chlorine_dioxide as water disinfectant

8/10/2019 Chlorine_Dioxide as Water Disinfectant

1/183

chlorine

Dioxide

as

a

potable

water

Disinfectant:

Application,

Residuals,

and

By-products

Monitoring

Justin

Michel

Rak-Banville

A Thesis

submitted

to

the

Faculty

of

Graduate

Studies

of

The

University

of

Manitoba

in

partial

fulfilment

of

the requirements

of

the

degree

of

Master of

Science

Department

of

Civil

Engineering

University

of

Manitoba

Winnipeg,

Manitoba,

Canada

Copyright

O 2009

by

Justin

Michet

Rak-Banvilte

by


2/183

THB

UNIVBRSITY

OF

MANITOBA

FACULTY

OF

GRADTJATE

STUDIBS

COPYRTGHT

PBRMISSIOhI

chlorine

Dioxide

as a

potable

water

Disinfectant:

Application,

Residuals,

and

By-products

Monitoring

B),

Justin

Michel

Rak-Banville

A Thesis/Pl'acticum

subrnittetl

to thc

Faculty

of

Gratluate

Stuclies

of Te

Universitv

of

Manitoba

in partial

filfillnent

of

the

requirenre

llt

of

te degr.ce

of

Master of

Science

Jusfin

Michel

lla

k-BanvilleO2009

Pcrlnission

has

bce.n gralrted

to the

Univcrsity

of

Manitoba

Litrr:rries

to

lend

r

coll]

of

this

thesis/pr:rcticum,

to

Libr:rr.v

rntl

Archives

Canada

(LAC)

to lentl

copy

of

this

thesis/rracticum,

and

to

LAC's

gent

(UMI/ProQuest)

to

tnicrofilm,

sellcories

ancl

to

publish

an

rbstract

of this

thesis/prncticu

m.

This reprodtlction

or

copY

of this

thesis h:rs

bee

r mrde

rvailable

by

authorit-v of

the

copyright

olrner

solely

for

the purpose

of

rri'ate

stucr-v

rnd

.csearch,

anrr

mrv

nrv

be

reprod*cett

:rna

copied

as

permitted

b' coryl'ight

larvs

or rvith

express

n,rittcn

ruthorizrtion

frorn

te

cor1,rigt

on,'r.


3/183

Author's Declaration

I

hereby declare that

I

am the sole author

of this

thesis. This

is a

true

copy

of

the

thesis,

including

any

required final

revisions,

as accepted

by

*y

examiners. I understand

that

my

thesis rnay be

made

electronically

available to the

public.


4/183

Abstract

The

objectives

of

this

work

where

to

study the effectiveness

of

the standard

DPD

(N,

N-diethyl-p-phenylenediamine)

method's for

the detection of

chlorine

dioxide.

This

included

evaluating

calibration

using

potassium

permanganate

and alternative

free

chlorine

masking

agents, diethanolamine

and triethanolamine. Additional

objectives

included

the

development

of

suitable spectrophotometric methods alternative

to

DPD

from which a new detection

platform

could

be

established. Candidates

such

as

N,N,N',N'-tetramethyl-p-phenylenediamine

(TMPD),

alizarin

red

S

(ARS),

and

copper(Il)

sulfate

were selected.

Results

suggest

that

calibration

of

DPD using a

potassium permanganate

surrogate is

susceptible

to temporal

changes, whereas

use of diethanolamine and

triethanolamine

as

a free available chlorine mask

proved

to

interfere

with

DPD chlorine

dioxide

testing.

Use

of

Alizarin red

S

provided

a

detection mechanism

for

chlorine

dioxide

(0-4

ppm)

in the

presence

of low concentrations

of chlorite ion

(0.2

and

0.5

ppm).

Detection

of chlorite concentrations

using

copper(Il) sulfate

were

established for

chlorite

concentrations

ranging from to

6

ppm

to

10

ppm

which is much higher than regulated

residual

concentrations

in drinking water. Lastly, the

combination

of

TMPD and

cerium(IV)

provided

for residual chlorine dioxide analysis

in

concentrations less

than I

ppm.

111


5/183

Acknowledgements

Many

thanks

to

Colleen Prystenski

for

reading

my

essays

on

these

topic,

specifically

taking

the time and

trouble

to

alert

me to errors and

providing

a

professional

copyreader's

job

on

my effor-prone

prose.

Many

thanks to

rny

friends, family,

and

colleagues

at

the University of Manitoba.

In

particular

both the Department

of

Civil

Engineering: Yick

Fung

(Steven)

Cho

and

Arman

Vahedi

for their

support

and

numerous

consultations on

the

topic of

potable

water;

and

to

the

Department of

Chemistry:

Matt

Pilapil, for

graciously

validating

our

conversations

of

analytical chemistry,

more

speciflrcally

the

use

of electrochemistry.

Special thanks

to my advisor,

Dr.

Beata Gorczyca

(University

of

Manitoba),

and

my

examining

committee,

Dr.

Norman

Hunter

(University

of

Manitoba),

Dr.

Tricia

Stadnyk

(University

of

Manitoba), Dr. Kim Barlishen

(Manitoba

Office of

Drinking

Water),

and

Dr.

Peter Hombach

(Osorno

Enterprises

Inc.) for not only

providing

guidance,

but

also rigorously scrutinizing

my work

and substantially

improving

its

quality.

Thank

you.

iv


6/183

Dedication

I

would

like

to

dedicate this

work

to

the

researchers

of chlorine dioxide,

and those

dedicated

to

improving the

quality

of

drinking water through a multidisciplinary

team

approach;

to those whom

have come and

gone

and

to

those

who

will

hopefully

build

on

this

work.


7/183

Table

of

Contents

AUTHOR'S

DECLARATION

................ II

A8STRACT..............

.............

III

ACKNOWLEDGEMENTS.......

............. IV

DEDICATION.........

................V

TABLE OF

CONTENTS ......

VI

LIST

OF

FIGURES............

.................XIIr

LIST

OF

TA8LES............ ..

XVI

LIST OF

ABBREVIATIONS............... XVII

PART

1: RESEARCH OBJECTMS......... ............21

Cgeprpn

1

: PnoersN,l

SrersNpNT............... ..........21

PART

2: LITERATURE

REVIEW.

.......2s

CrnprBR

2

:

Porlsr-e

W,q,rsn

DIsnrFpcloN.............

...............25

2.I

A Brief

Review

of

Chlorination...........

...........25

2.1.1 Chemistry of

Chlorination

.....28

2.l.2Breakpoint

Chlorination

.........

................34

2.1.3 Chlorine

Disinfection

By-products

.........37

2.2 The

Alternative Disinfectant: Chlorine

Dioxide.....

.........40

2.2.1Chemistry of Chlorine

Dioxide.... ...........40

VI


8/183

2.2.2

Chlorine

Dioxide for Drinking

Water

Treatment. .....47

CTLqpTpR

3

:

EveIueTION

OF

CuRRgNT ANALYSIS

METFIODS FOR CHLORINE

DIOXIDE

AND

lrs

Bv-pRopucrs

...........

................51

3.1 Monitoring Methods

Availablefor

Chlorine Dioxide, Chlorite, and Chlorate...5I

3.1.1 Current Conditions of Chlorine

Dioxide

Use

in North America

.................52

3.1.2 Current

State

of

Analyses............... ........53

3.i.3

Basic Spectrophotometric Analysis of Chlorine Dioxide

(Operator

Based) 53

3.L.4Practical

Operator Spectrophotometric

Methods

......56

3.1.5

Acid

Chrome

Violet K Method. ..............61

3.1.6 Amaranth

Method..............

....................61

3.1.7

Chlorophenol

Red

Method............... .......62

3.1.8

N,N-Diethyl-p-phenylenediamine.......

.....................62

3.1.9 Lissamine

Green

B

and

Lissamine

Green

B Horseradish Peroxidase..........63

3.1.10

Rhodamine

8..............

.-.......64

3.1.i 1 Instrumental Methods

(Other

Than Spectrophotometric)..........................64

3.L.I2

Amperometry

(Operator

Based)..

..........66

3.1.13

IonChromatography(CommercialLaboratoryBased) ............68

3.I.I4

On-Line

Detection

(Operator

Based)

.....................69

3.1.15

Standards,

Glassware and

Sample

Preparation............. ...........7I

3.2 General

Method Acceptonce

and

Adoption.............

........74

3.2.1 Trends

in Regulator Acceptance ...........

...................76

vii


9/183

3.2.2BriefReviewofRegulatoryMonitoringMethods...............

......77

CHRpreR

4 : Rvrnw

oF

REGULAToRv

RrqunEuENTS

PERTAINTNG

To

CHLoRTNE

Droxro

DrsrmpcuoN.............

..............80

4.1

Provincial and

Federal

Regulations

in Canada.....

.........82

4.1.1 Provincial

Regulations.........

...................83

4.1..2

A Canadian

Perspective

.........87

4.2 United

States

Environmental

Protection

Agency

(EPA)

Regu\ations.................89

4.2.1

Ohio

Environmental

Protection

Agency...............

.....................91

4.2.2 California Department

of Public

Health

...................94

4.3

European

Union

Regulations...............

.........96

4.4

Regulationsfor

Selected Countries..

..............98

4.4.1,

United

Kingdom

....................98

4.4.2

Germany ............

...................99

4.4.3

Australia...........

...................

100

4.4.4 New Zealand

......102

4.5

The World

Health

Organization

QTrHO)

......105

Cnprn

5 :

IrupnovrNc THE

AccuRecy

oF

N,N-DrETIryL-p-pHENvLENEDTAMTNE

(DPD).......

......... i06

5.1

An Introduction

to

DPD

.............107

5.2

The

Chemistry

of

DPD

...............109

5.3 Recommendations

Regarding

the

Continued

Use of

DPD.....

.........11I

vlll


10/183

5.4

Investigations of the

Calibrationfor the

Standard

DPD

Chlorine

Dioxide

Method ..........I12

5.5 Spectrophotometric

Agents

Alternative

to

DPD

for

Potential Operator

Use

...I I3

5.5.

1 Use of

N,N,N',N'-Tetramethyl-p-phenylenediamine

(TMPD)

and

Cerium(IV)

for

Detection of

Chlorine

Dioxide............ ...113

5.5.2 Use

of

1,2-dihydroxyanthraquinone-3-sulfonate

(Alizarn

Red

S)

for

the

Detection

of

Residual

Chlorine

Dioxide in

the

Presence

of Chlorite

as

an

Interference...............

...................116

5.5.3 Use

of

Copper(Il) Sulfate

for

the Residual

Detection

and

Discrimination

of

Chlorite

from Ch1orate............ .....1I7

5.6

Free

Chlorine

Masking

..............117

5.7 Masking

Agents

Alternative to Glycine. .......119

5.8

Examination

of Using an

Alternative FAC Masking:

a

Mixture

of Di- and

Tr

Ethanolamine.............

..... 122

PART 3: EXPERIMENTAL

.................123

CrnprpR 6 :

GBNgRaL MATERIALS AND

Mernoos .................I23

CHeprpn

7

:

DPD

FoR

CHLoRTNE DroxrDE ANALysrs............... ...............124

7.1

Experimental

Methodfor

Analys

of

Colibration

using DPD

for

Chlorine

Dioxide

..........124

7.2

Materials

and Reagents

(Analysis

of

the

DPDfor Chlorine Dioxide Method

Calibration)

...124

IX


11/183

7.2.T

Experimental

Method for

Use

of

Diethanolamine

and

Triethanolamme

as an

Alternative FAC Mask .................125

l.2.2Materials and Reagents

(Alternative

FAC Mask

Experiments).............

....126

CuepreR

8

: PorgNrrel

SppcrRopHoroMErzuc

Cnr-oRr,rp

Droxloe DErEcrroN

MsrHoos AlrnRNRrrvE To

DPD

(OrnneroRs

BASED)............. ..............128

8.1

Alternative Spectrophotometric

Methods

for

Chlorine

Dioxide Residual Anolysis

Research

........

128

8.1.1

Materials

and Reagents

of

Alternative

Spectrophotometric

Work ............I29

8.1.2

Experimental Work for

Chlorine

Dioxide

Residual Detection

using

TMPD

and

Cerium(Iv).......... ..................129

8.1.3

Experimental for

the Detection

Chlorine

Dioxide

Residuals using Alizarin

Red

with

Chlorite as

an

Interference......... .....130

8.1.4

Experimental for

the

Measurements

of Chlorite

Concentrations with

Copper(Il)

Sulfate

.......130

PART

4: RESULTS AND DISCUSSION...........

...131

Crm.prsn 9

:

ON

THE

UsE

oF

DPD

FoR

RESTDUAL

CHLoRTNE

DroxrDE

DprpcrroN ....131

9.1 Observations

Using

Potassium Permanganate

for

DPD Calibration.............. 13I

9.2

Calibration of the

DPD Method

Using Potassium

Permanganate...................134

CTnpTBR

iO

:

AN AITnRNIIVE

FAC MesT

FoR CHLoRINE

DIoXIDE

DPD

ANeIysIs

.........136


12/183

l0.l Observations

on the

Use

of

Di-

and Tri- ethanolamine

(DEA

and TEA)

as an

Alternative

Masking Agent........ ....... 136

10.2

Discussion of

Using

DEA and

TEA as

Prospective FAC Masking Agents

.....

142

CrnprpR

i I

:

NovslUsn

or

TMPD

AND CERTUM(IV)

Eon

Sue I

ppM

CHLoRTNE

DroxlB

Dprpcrrou

...........144

I

1

.

I The Results

of Using TMPD and

Cerium

for

Chlorine Dioxide Detection

... .. I 44

I

1.2

TMPD

and Cerium

Detection System

for

Chlorine

Dioxide .........

I50

CHRpTSR

12

:

Usn

op

Alzennq

RBo

S

FoR CHLoRINE

DIoXIDE

DETECTIoN

IN

THE

PResBNc

oF

CHLoRTTE

.............

..........L52

l2.l Results on

the

use of

Alizarin

Redfor

Chlorine

Dioxide

Detection

in

the

Presence

of Chlorite .......

152

12.2

The

Alizarin

Red

S Systemfor Chlorine Dioxide..... ....

154

CHeprER

13

:

DprpcrroN

oF

Curozurs

FRoM

Cnr-oRerp Uswc Coreen(Il)

SurrRre

.........155

I

3.I Findings

from

the

use

of

Copper sulfate

for

Chlorate

Detection

in

Presence

of

Chlorite

......... I55

13.2 The

Copper(Il)

Sulfate

Systemfor

Chlorite..... ............ I57

PART

6: CONCLUSION .....159

CHaprsR

14

:FrNer-Tuoucurs

...........159

PART

7:

RECOMMENDATIONS .......163

CneprER

15: PorBxuALDrRECTIoNS........... ........163

XI


13/183

I5.l

Suggestionsfor

the

Continuation

of

Additional

Experimental \ork..............164

I5.2

Chlorine

Dioxide

in Manitoba............... ....165

15.2.1Efforts

to

Reduce THM

Content:

Use

of Chlorine

Dioxide

and

DOC

Reactivity.

...................

165

15.2.2

Residual Analytical Detection ............

i66

APPENDIX

A: Tabulated

US EPA

Methods

for

Chlorine

Dioxide,

Chlorite

and

Chlorate,

June

2008 ..............168

APPENDIX B:

Raw

Experimental Data From

The

Investigation

Of

Using

DEA

and

TEA

as a FAC

Suppressant.............

......170

REFERENCES ......... ............175

xll


14/183

xl11


15/183

Figure

12: The

molecular

structure

of

ARS. .............. 1

16

Figure l3: Both

acetone and

DMSO

have

shown

FAC masking characteristics,

yet

similar results for

a

selenium substitute

have not

been

found.

....I22

Figure

14:

The

structures

of both DEA

and

TEA. ........ ..............122

Figure

15: Gas

train

setup

for the

generation

of chlorine dioxide. The collected

gas

was

bubbled

through

water, collected,

and

standardized

........ ...........I27

Figure

16: Results

of

using

KMnOa

as a

chlorine dioxide

surrogate

for DPD calibration.

.........r32

Figure

17: Spectroscopic

calibration

of

a surrogate

oxidant

to

provide

a correlation

between

chlorine

content and

absorbance,.........

........I37

Figure 18:

Observed

Trends in Varying both the

Oxidant

Ratios, as well

as, the

Masking

Agent

Ratios.

.........142

Figure l9:

A

comparison between

a

solution of

TMPD in

water,

and

its oxidized form

using

chlorine

dioxide.....

........I45

Figure

20:

Observed

changes

in

absorbance

from substituting TMPD for DPD in

Standard

Methods.

..................146

Figure

21

:

Effects

of

increasing the chlorine dioxide

content when using

TMPD for

detection

at

612

nm............ .....I47

Figure

22: Wavelength selection comparing results from the inclusion of cerium,

and

without. .................148

xlv


16/183

Figure 23: Application of a

potential

TMPD

and

cerium

system

for residual chlorme

dioxide analysis,

....149

Figure 24: Comparison

of incorporating

cerium with

DPD

and

without

......150

Figure 25: UV/Visible spectrum of alizarin red, buffered to a

pH

of 7.7,

absorbance

readings were

taken at 516nm.

.................152

Figure

26: The

observed

reduction in

absorbance

at

516

nm

due

to increasing

concentrations of chlorine dioxide used. ...................153

Figure

27: Use

of alizarin

red

for

chlorine

dioxide

detection

with

and

without potential

chlorite

interferences. ............ ..................I54

Figure 28:

Observed

non-linear

increase

in

spectrum absorbance

frorn

increasing

chlorite

concentrations tested.. .............156

Figure

29: Molar absorptivity constant calculations

based

on low

and

high chlorite

concentrations............ .............157

XV


17/183

I-ist

of

Tables

Table

i: Select

temperatures

and

their computed

effect on the equilibrium

constant

of

the

hypochlorite

ion. Values calculated based on

ionization

constants

................31

Table

2:

Selected

properties

of

chlorine

dioxide,

data

adapted

(Kirk,

et

al.,l99I)..........41

Table 3:

Standard

reduction

potentials

of

several

oxidation

states

of

chlorine at

25'C, data

adapted

(Lide,

1999).

................43

Table

4: Common disinfectants

and

their

associated

oxidation

values at25'C................46

Table 5:

Various chlorine dioxide

reactants and

non-reactants

commonly found

in

raw

waters.......

...............51

Table

6:

Maximum

wavelengths and

molar absorptivities

of

common

interfering

oxychlorine

compounds.

Molar absorptivities

are

presented

as

(moVl)-t

cm-t,

tabl"

adapted

(Gates,

et

al.,2009).......

.......

.......54

Table 7:

Meta-Analysis of

Tabulated Photometric Methods

for

Detection

of

Chlorine

Dioxide.....

...............59

Table 8:

Meta-Analysis of Noted Interferences

Tabulated Photometric

Methods

for

Detection

of Chlorine

Dioxide.

..................60

Table 9: Meta-analysis of

national

and

international

regulations

for chlorine

dioxide,

chlorite

and chlorate.

..............

...................83

Table

10:

Tabulated summary comparing current

Manitoba

regulations

to

those

of

other

Regulators

...............89

xvl


18/183

Table

1

1:

The

rate of

change

for the

calibration of

DPD

using

KMnOa at

0.025,0.5,0.75,

and

1.0

ppm..........

..................

134

Table

12:

Estimation of chlorine dioxide

and

chlorine

content using

DPD

and

glycine

masking. ................138

Table

13: Results

of

the

potential

use

of O%DEA:100%TEA for FAC

suppression.

.....139

Table

14: Results

of

the

potential

use

of

25YoDEA:75%oTEA for

FAC

suppression.

.....L40

Table

15:

Results

of

the

potential

use

of 5OoloDEA:50%TEA

for FAC

suppression. .....I41

Table

16:

Results

of

the

potential

use

of

75o/oDEA:25%oTEA

for FAC

suppression.

....T41

xvii


19/183

List of

Abbreviations

ACVK

Acid Chrorne

Violet

K

ADWG

Australian Drinking Water Guidelines

ARS Alizarin

Red

S

AWWA

American

Water

Works Association

BSRIA

Building

Services Research and

Inforrnation Association

CDHP

California

Department

of

Public Health

CCD

Charged Coupled Device

CPR

Chlorophenol Red

CDW Committee

on Drinking Water

CT Contact

Time

DBP Disinfection By-product

DEA

Diethanolamine

DIN

Deutsches

Institut

flir

Normung

(German

Institute

for

Standardization)

DOC Dissolved Organic Carbon

DPD

N,N-Diethyl-p-phenylenediamine

DMSO

Dimethylsulfoxide

DDBR

Disinfectants/Disinfection By-products

Rule

DWA

Drinking

Water

Act

DWD

Drinking Water Directive

xviii


20/183

DWP

Drinking Water Program

EPA

Environmental Protection Agency

EDA

Ethylenediamine

EU

European Union

FAC

Free

Available

Chlorine

FACE

Free

Available

Chlorine

Equivalent

GAC

Granular Activated Carbon

GCDV/Q

Guidelines

for

Canadian

Drinking

Water Quality

HRP Horseradish

Peroxidase

IC

Ion

Chromatography

LGB

Lissamine

Green

B

LGB-HRP

Lissamine

Green

B

-

Horseradish Peroxidase

MAC

Maximum

Acceptable

Concentrations

MAV

Maximum

Acceptable Value

MCL

Maximum

Contaminant

Level

MCLG

Maximum

Contaminant

Level Goal

MRDL

Maximum

Residual

Disinfectant Level

MRDLG

Maximum

Residual

Disinfectant

Level

Goal

NHMRC

National Health

and

Medical

Research

Council

NOAEL

No Observable Adverse

Effect Level

NOM

Natural

Organic Matter

xix


21/183

NZDS

ORP

PAO

PCR

NTS

SPE

TDI

TEA

THM

tTHM

TMPD

UK

US

USEPA

UV

UV-VIS

wHo

New Zealand Drinking Water

Standard

Oxidation

Reduction Potential

Phenylarsine

Oxide

Postcolumn

Reagents

Sodium

Thiosulfate

Solid Phase

Extraction

Tolerable Daily Intake

Triethanolamine

Trihalomethanes

Total

Trihalomethanes

N,N,N',N'-Tetramethyl-p-phenylenediamine

United Kingdom

United States

United

States

Environmental

Protection

Agency

Ultraviolet

Ultraviolet-Visible

World Health

Organization

XX


22/183

Part

1:

Research

Objectives

Chapter 1: Problem

Statement

Chlorine

(Clz)

is

arguably

the most

cornmon

potable

water

disinfectant

used

throughout

North America. Although it is

important to

supply safe,

potable

water,

analytical

and

toxicological

research has

shown the

emergence

(since

the

mid

1970's) of

disinfection

by-products,

namely trihalomethanes

(THMs)

which

have been shown

to

cause adverse

reproductive

or

developmental

effects among

laboratory

animal testing

(World

Health

Organization

(WHO),

2008,

Clark

and

Boutin,

200I,

American

Water

Works

Association., 1990).

Consequently,

Regulators

are

now

actively curbing

THM

concentrations

in treatment

plants.

Driven by a low regulated THM content in

finished

waters,

the replacement of chlorination, in

favour

of adopting

chlorine

dioxide,

is

becoming

an

increasingly admired

scenario.

The

large

scale

use

and

acceptance

of

chlorine dioxide

has

routinely

presented

a

certain

magnitude of dissonance among

scientists,

engineers,

and

regulators. This

discord

is

presented

as

the

difficulty in achieving atargeted

dosage

level, without over

producing

by-products

(chlorite

and

chlorate) beyond regulated concentrations.

Particularly, the hypothetical

dosage

level which is

targeted

at meeting

oxidant

demand

and achieving

potable

water

disinfection

may

potentially

exceed current

guidelines

set

for

maximum dosages. The

exceedance

of

guideline

dosages

can

potentially

lead

to

the

subsequent

formation

of increased chlorite

and chlorate concentrations beyond regulated

by-product concentrations.

2l


23/183

Numerous chlorine dioxide

detection systems have been

proposed

throughout

the

last two

to three

decades,

with

sorne

being

more

effective

than

others. Of

those

proposed,

a few

have matured to

become standardized,

while

others

are simply

the

result

of

research studies

(Pepich,

et al.,

2007,

Hodgden and

Ingols,

2002,

Pinkernell,

et al.,

2000,

Hui, et

al.,

1997,

Xin

and

Jinyu,

1995,

Fletcher

and

Hemmings,

1985,

Knechtel, et al.,

1978).

These

growing research

interests

may be

considered

the result of concern

regarding

the adverse health

effects

of

THMs

in furished

waters.

In

particular,

as

THM

formation

has been shown to

be

linked to

the

use

of

free

chlorine, chlorine dioxide

does

not

produce

THMs

(Johnson

and Jensen,

1986)

and

has

become

an

attractive alternative.

A leading disadvantage to the use

of chlorine

dioxide

has been the

lack

of

available

established standardized monitoring and analysis rnethods to which regulators,

operators,

and researchers may refer.

This

situation

is

further complicated when chlorine

dioxide

is added

to

systems

which

cannot maintain a

residual

concentration, therefore

necessitating an additional

disinfectant such

as the addition of free

available chlorine

(FAC)

throughout the

treatment process

or

within

the

distribution

system.

It

is

the

combination

of

disinfectants

which can

proliferate

the multitude

of oxychlorine

species

present

in

these

waters leading

to analysis interferences. These include chlorine dioxide,

chlorite,

chlorate, FAC, and corrbined

chlorine

which

either

exist as a

residual

concentration or

by-products arising from the

use of

a mixed

chlorine

dioxide and

free

chlorine

treatment

process.

Therefore,

any

detection

system

(specifically

the

chromophoric

reagent) designed for

a

particular

oxychlorine species must be, at

minimum, sensitive

to fypical

residual concentrations

(sub

I

ppm

range), but

also

provide

22


24/183

the necessary selectivity

among

comon

interferences

and

reproducibility

required of

such

a

method

which regulates water

for

human consumption.

An

ideal

method

would

provide

operators with

an

inexpensive

daily

routine

(including quality

control calibration) of which is

straightforward, non-labour

intensive

and

reproducible;

these

demands largely limit such

development

to spectrophotometry.

'While

there are

a

multitude

of

generator

designs which

exploit

different synthesis

reactions,

both

regulators

and operators must be aware of

generator

purity

and

potential

by-products

introduced

which may affect the adoption of a

particular

analysis method.

Though such

criteria

suggest

the

benefits

of

on-line

chlorine dioxide and

chlorite

selective electrodes, for the most

part,

North American regulators have

yet

to adopt

such

methods.

Efforts

to eliminate

current drawbacks to the use of chlorine dioxide include

improvements

to

current

field

detection methods and regulations

which not

only

approve,

but

also encourage such developrnental use.

As

such,

the

use of standardized EPA

approved methods

for

residual analysis,

on-line

real-time

amperometric

sensor

based

monitoring

systems, and

discontinuance

of

the reliance

on DPD

are

all initial, but crucial

steps,

to

developing

chlorine dioxide

as

not

only

a THM-solution,

but also a

small

economic treatment

center

disinfectant.

Consequently,

the reliance

upon

spectrophotometry

for both the

selectivity

and

sensitivity

required to

determine

low levels of chlorine dioxide

in

the

presence

of

chlorite,

FAC,

chlorate,

and other

species

requires extensive research

and

testing.

This

manuscript

presents

three spectrophotometric reagents which

exhibit

potential

for fuither

23


25/183

advancement

and

prospective

development of

a

spectrophotometric

method alternative to

DPD for detection

of chlorine dioxide

and its by-products.

The

principal

focus

of

this

research was to study the effectiveness

of

the standard

DPD method

for

the detection

of

chlorine dioxide

in

potable

waters,

including an

evaluation

of

the

spectrophotometric

calibration using

potassium

permanganate. The

fundamental

theory

supporting DPD

for chlorine dioxide involves the incorporation of

the

FAC

rnasking

agent

known

as

glycine,

which

when

reacted,

forms

a

non-oxidizable

product. Through the elimination

of FAC

(via

the formation

of

non-oxidizable

product,

ie. "masking"),

the

potential

for

reaction

between

FAC

and

chlorine

dioxide is

negated,

and in

turn,

provides

DPD

to

be

the

sole

reactant for

chlorine

dioxide. This rnasking

is

the basic

theory which effectively

gives

rise

to

the DPD detection

rnethod

for

chlorine

dioxide.

Though

this

fundamental supposition

is

debated in

literature,

and typically

there

exist

other oxidative

candidates in

water

sources

(ranging

from

metal

ions to other

oxy-

chlorine

species, or

even

potentially

oxidative

pharmaceuticals),

studies

investigating

alternative masking

agents

which exhibit

potential

for

a

wider

spectrum

of

masking

are

warranted.

This research

included evaluating

the

use

of an

alternative

masking

agent

consisting

of a

mixture

of both

diethanolamine

and triethanolarnine which was

hypothesized

to

completely rnask

FAC,

and

potentially

other

oxidative

species

excluding

chlorine

dioxide.

Finally, the development

of

potential

alternative

spectrophotometric reagents was

explored to

provide

a foundation

for

further research. Promising candidates, such as

alizarin red,

copper(Il)

sulfate,

and N,N,N',N'-tetramethyl-p-phenylenediamine were

investigated

for their

potential

to

measure

chlorine dioxide

and chlorite for typical

24


26/183

drhking

water

treatment residual concentrations

(sub

lppm). To

carry

out

these

objectives,

current available

data

and

literature

pertaining

to

the current

use of

chlorine

dioxide

as

a

drinking water

disinfectant,

its

popularity

among North America, and

analytical

residual measurernent

methods available

for

Regulators

to

rely upon were

compiled.

Part 2:

Literature

Review

Chapter

2: Fotable

Water

Disinfection

2.1

A Brief

Review of

Chlorination

Safe

potable

water

for consumption is

indubitably

a critical necessity of all living

organisms. On

a

cellular

level, water

acts

as a

plasma

to

support cellular

functions,

yet

on

a

systemic

or social level, water sources

are

required for

a

plethora

of civic and

industrial

purposes.

Throughout the

history

of human

existence,

civilizations have

consistently been

rooted and

established

in close

proximity

to

large bodies

of water.

Between

evidence

of

unref,med charcoal

filtering

systems

in

India

as early

as

2000 BC

(Bagwell,

et al.,

2001)

and

the

complex

architecture

of

the Roman Aqueducts

which

date

back

to

I97

BC

(Fagerberg,

et

a1.,2006)

it

is

easily recognizable that

even these

earlier

populations

were capable of identiffing the importance

of

water.

Further recognizable

is

the increasing demand for large

quantities

of

this

natural resource

for

consumption, as

well

as

other

use

which

have f,rrther

spurred

the

exploration

of

new

or

alternate water

sources

that coincide

with

population growth.

It

is apparent

that not only ancient

civilizations, but

also contemporary

cultures

have

long understood the rnerit

of

accessing

25


27/183

large

quantities

of

water

to

support

the

needs

of

their

societies.

Despite

this, the

emphasis

throughout the

greater part

of human history

has been

placed

more on securing

large

quantities

of water rather than monitoring or treating the

quality

of

these

sources

to

prevent

the

spread of

water

borne

diseases.

Historically, one of

the

earliest

disinfection

methods

recognized

for its continued value

calne from

Hippocrates'

work

and

admonition

that water

should

be boiled

prior

to

consumption

or

use in

order

to achieve

potable

waters

(Bagwell,

et

a1.,2001).

History has

provided

documentation detailing organoleptic

problems

associated

with the

quality

of drinking

water

sources, specif,rcally

turbidity,

taste

and

smell. The

realization

that basic techniques such

as

reliance on the use

of olfactory and

gustatory

reflexes to

judge

water

quality

are

inadequate is

a

fundamental maturation step

for the

development

of the drinking water disinfection and education

processes.

The

established

relationship

held between drinking water, water born

diseases and consequent

death

have

forced societies

to

develop

our

knowledge base

for disinfection

and

further advance

technologies

for

the

treatment

and

prevention of

drinking

water

contamination.

Among

these

technologies, the

application of chlorine

(Cl2)

has

arguably

been the

rnost

widely

used

disinfectant in

Canada

and

the

United

States

(US)

for

nearly

the

past

90

years.

The disinfection

of

drinking water

has been

credited

with

increasing life

expectancy

throughout the

past

century

by

as

much as 50

percent (Simonovic,2002).

The

f,rst

documented chlorination occurred in 1850, by John Snow in

his

attempt to

disinfect

the

Broad

Street Pump

water

supply in

London

(England)

following an

outbreak

of cholera.

By 1897, Sims Woodhead synthesized

a

dilute

sodium

hypochlorite

(NaOCl)

solution

as

a temporary countermeasure

to

sterilize the

potable

water distribution mains

26


28/183

in Kent

(England)

in

response

to

a

typhoid

outbreak

(Irwin,

et

al., 2006). The

success

of

Woodhead's

counter measure was

evident,

as

the response was a remarkable decrease

in

the number

of

deaths associated with

typhoid,

leading

to wider

adoption

throughout

Great

Britain by the turn of the century. Shortly after, the first large-scale chlorination

protocol

was

developed and carried

out by

the

Jersey City

Water

Works

(New

Jersey, U.S.)

in

1908

(Irwin,

et al., 2006).

As

more

water

distribution systems

slowly

adopted

the

procedure

of chlorination,

a subsequent decrease was observed

in

the death toll

primarily

due

to

the cholera,

typhoid,

dysentery and hepatitis A associated with water born

diseases

(American

Water Works

Association.,

2006).

This

decline

made

possible

the

disappearing

transition

of a mortality

"penalty"

associated with living

in

congested urban

areas.

The

resultant

reduction

in

lives lost from 25

to

1

in 100,000

people

proved

signif,rcant

(Arrnstrong,

et

al.,

1999).

Thus,

consistent with

Hippocrates' theory

that

the

quality

of

water is linked

with

public

health, current

research suggests

that

clean

water

was responsible for nearly

half of

the

total mortality

reduction

in

rnajor cities, three-

quarters

of

the infant mortality

reduction, and

nearly two-thirds

of

the

child

mortality

reduction

(Cutler

and Miller, 2004).

Furthermore,

Culter estimates

that the

social

rate of

return

on the

disinfection

of drinking

water

was

greater

than

23

to I with a cost

per

life-

year

saved by

clean

water of

about

$500

in 2003

dollars.

This

dramatic

reduction in

rnortality

is

regarded

as

one of

the

most

important

advances for

public

health

and safety

of

the

21't century.

27


29/183

-

Mortality

1900 1910 1920 1930 1940 1950

1S60

1970 1980

Year

Figure

1:

Global

typhoid mortality

rates

exemplifying

the effects of

large

scale chlorination,

fgure

adapted

from American Water Works

Association,

2006.

One of the

greatest

advantages

gained

from

the use

of

chlorine is the

ability

to

effectively

achieve a broad-spectmm

germicidal potency,

while

simultaneously

allowing

for

residual

disinfection throughout drinking water distribution systems.

Furthermore,

chlorine

also

permits

the

control of

various taste and

odour

problems

via

the

chlorination

of problem

substrates such as algae,

decaying

organic

matters,

manganese,

iron,

sulphur,

nitrogen

and ammonia containing

compounds.

2.1.1 Chemistry

of

Chlorination

The

mechanism of

chlorination

begins via

the hydrolysis

of

either

liquid

or solid

sodium

hypochlorite

in

solution

(NaOCl),

or

gas

chlorine

(Cl2)

upon

contact with water,

producing

a

pH

dependent

equilibrium mixture

of

chlorine ion (Cl-),

hypochlorous

acid

(HOCI)

and

hydrochloric acid

(HCl).

Chlorine

gas

undergoes

the

following hydrolysis,

equation

(l).

a

32

30

c28

326

7zq

9.-zz

820

3,u

?16

u

(512

.

10

(Eu

L^

oo

2

0

Global

Typhoid

Mortality Rates

From 1900 to 1980

Onset of

public

water chlorination

28


30/183

CIr,r, * HzO--

HOCI

,,nr+HCl

(1)

Equation

(1)

is then

followed by

the

partial

dissociation

of

the weak

acid,

hypochlorous

acid,

to

the

hypochlorite anion,

presented

in equation

(2).

HOCI

@+-----+

H* +

OCI-

(2)

The combination

of

equations

(1)

and

(2)

is the

prevailing

reaction for a

low

pH

range,

which

results

in

the formation of chloramines from

the

presence

of

nitrogen

containing

organic

matter,

in

part

due

to the acidity of

hypochlorous

acid. As

most

drinking

water

sources

fit for consumption range higher thana

pH

of

4,the

result is

the

displacement

of

the equilibrium

to

the right, forming

more hypochlorite,

subsequently

minimizing any avallable

hypochlorous

acid.

This is

expected

as

the

pH

approaches

the

pKa (pKa1ocr:

7.5). As

evident

in

both the

above equations

(1)

and

(2),

the amount to

which

the

hypochlorous

anion will dissociate

is strongly

associated with the system's

pH.

These equations

can describe

two

conmon treatment

scenarios;

the

set

describe

the

hydrolysis

of chlorine

gas

forming

hypochlorous

acid,

whereas

the later describes

the

addition

of liquid sodium hypochlorite.

The hydrolyzation

of

chlorine

gas

relies upon

the

equilibrium

constant

as

follows

(equation (3)).

K":

luoct][s.][ct

]

:4.5x10a

(moVL

atm)

at

25'

C

(3)

Ict,]

As

equation

(3)

suggests,

a

large

equilibrium constant

provides

for the

notion

that

large quantities

of

chlorine

gas

may dissolve

in water.

Equation

(2)

further

defines

the

displacement

of hypochlorous

acid

(HCIO),

to

the hypochlorite ion

(describing

the

addition of

sodiurn hypochlorite)

as

follows.

29


31/183

[n.llocr I

K

:L

-

lL

-

l:3x10-8

Mat25"C

oct

LHocl]

(4)

Thus

any equilibrium concentrations established

will reflect differing

concentrations of

the

products

due to the

pH,

and

are

presented

in

Figure

2.

Typical natural water

pH

range

pH

Figure

2:

Distribution

of

Cl2,

HOCI,

and OCI-

as

a

function

of

pH

in

pure

water.

Though

the

effect of

temperature

on the equilibrium constant for equation

(4)

may

appear subtle,

the trend

becomes more evident when several constants are compared

at

once,

as

computed

and

illustrated in Table

1.

30


32/183

Table

1:

Select

temperatures

and

their computed

effect

on

the

equilibrium

constant of

the

hypochlorite

ion. Values

calculated based on

ionization

constants.

Temperature

('C)

Kocr-

pKaocr-

1x1o-08)

0

5

t0

15

20

25

30

35

40

45

50

1.36

1.56

1.79

2.05

2.33

2.63

2.97

3.33

J.t3

4.t5

4.61

7.868

7.806

7.746

7.689

7.633

7.580

7.s28

7.477

7.429

7.382

7.336

The distribution between hypochlorous acid

and

the hypochlorite ion

gives

rise to

the notion of

free

available chlorine

(FAC),

a

term

commonly

used

throughout

drinking

water disinfection

plants.

Upon

the

addition of

hypochlorous

acid to water

(referred

to

as

chlorine), initial

reactions

proceed

first with both organic materials and

various

metal

ions -

those with an

oxidative

capacity

- which

subtract

from the

initially

applied dose.

Such

chlorine is often

not available

for disinfection.

The chlorine remaining

following

disinfection is

referred

to

as

the

total chlorine residual. This total

chlorine

residual

may

then

be

further

subdivided

into the

following

categories: combined chlorine and free available chlorine.

The combined

chlorine

accounts

for

the chlorine

which has further reacted with

additional

substrates, such

as

ammonium

ions,

nitrites, nitrates, etc

for a

given period

of

contact time

(CT).

The

remaining

chlorine, known as the FAC,

is

the amount of

hypochlorous acid

and

hypochlorite ion available to further inactivate the

proliferation

of

disease

causing

bacteria

and organisms. The FAC

parameter

is a

standard monitoring

31


33/183

measurement of

potable

waters. As

such,

taking into account the

relative

distribution

of

both

hypochlorous acid

and hypochlorite ion at different

water

pH's

is

important

as

the

disinfection

capacity of hypochlorous acid

is

greater

than that of the hypochlorite

ion.

White

notes

that

hypochlorous

acid

is

considered to have more

biocidal

activity than the

hypochlorite

ion, as

it

can easily

penetrate

microbial cell walls due to the lack of a

charge. When

compared the hypochlorite ion's negative

charge

interfering

with

cell

wall

diffusion,

hypochlorous acid is

generally

thought to

provide

significantly more

disinfection

potential

(White,

1986). The consequential distribution of hypochlorous

acid

at

varying

temperatures

must

be

accounted

for

when

designing

a

treatment

process

targeted

at

a

specific FAC

value.

The theoretical hypochlorous acid distribution may

be

calculated

at a

given

temperature, as

shown

in Table i

and equation

(6)

under

ideal

circumstances

involving

pure

water

and

no chlorine

demand.

Substituting equation

(4)

into

equation

hypochlorous acid

at a

given

temperature

and

pH

Ratioof

HOCI:

(5),

the

ratio of

hypochlorite

is

elaborated in

equation

(6).

I

ion

to

(s)

(6)

,

*Kor, /

l* Korr

tloP,

r I

/w-l

As a further impediment

in

the

goal

of achieving a specific FAC, side reactions

with

ammonia are a cormon occurrence, and are even

more

of

a concern for

the small

groundwater

treatment

plants

throughout

Manitoba

experiencing elevated

levels

of

ammonia.

As

hypochlorous acid is an oxidizing agent,

it

will

react with ammonia

present

32


34/183

in the water, effectively

increasing the combined

chlorine

and

reducing the targeted FAC

value.

The

increase in combined

chlorine can be

explained

through the successive

formation of

monochloramine

(NHzCl),

dichloramine

(NHCI2)

and nitrogen trichloride

(NCl3).

Their formation, specifically their rate constants

and

temperature

dependencies,

are expressed

in the

following equation set

(Ozekin,

et a1.,1995,

Valentine,

et al.,

1988).

The formation

of

nitrogen trichloride, equation

(9),

is

known to

predominantly

occur at a

pH

less

than

4.4

and

relatively slowly;

rate constants have been reported

for

this reaction

at specific

temperatures although no

forrnation

of

a

rate constant-temperature dependent

equation

was

found,

in contrast

to

equations

(7)

and

(8)

(Asano

,2007).

NH,

+

HOCI

-------+NHrCl

+ H

,O

krr.r,

:2.37

xl0t2 eetstIlr)

(M-'ht)

NH,CI

+ HOCI----->NHC\.+ H

rO

k,na.

:1.08r10ee(-20r0/r)

(Art-t-t,

NH2CI

+

HOCI

-------+

NCl.

+

H

,O

(pH

N|-+SH*

+3Ct- +3HrO

(10)

Stoichiometrically calculated,

the

chlorine

to ammonium

ratio at

breakpoint is

expected

to

be

7.6:

I

(rnass

basis) and

a

mole ratio

of

1.5:1.

Forecasting

breakpoint chlorination

parameters

based

upon

the

ammonia content

in water

has been

previously

studied

(Minear

and Amy, 1996, Pressley, et

al., 1972),

allowing

for experirnental

results

to

be

compared

with relative confidence.

In water

sources

where

the ammonium ion was the sole contributor to the chlorine

demand,

breakpoint

chlorination

was

observed

in

a

ratio

of

8:1 by

weight

for

chlorine

to

ammonium

in

a

pH

range

of

6-7

(Wolfe,

et

al., 1984). It

has

been noted that this

ratio

is

only

valid for

ammonium

concentrations

lower than

lppm,

likely

due

to

the reaction

rate

being

a

function

of

initial

ammonia content

and can

range

from minutes

to

hours

for

a

given pH

and

temperature.

36


38/183

2.1.3 Chlorine

Disinfection By-products

It was n 1974

that Bellar

and

Lichtenberg,

followed

by

Rook, confnmed

that

the

use of

chlorine

based

oxidants, such as chlorine,

for

the disinfection of drinking

water

resulted

in

the

presence

of

chloroform (a

suspected

carcinogen),

and

other

undesirable

disinfection

by-products

(DBPs)

in

potable

waters

(Rook,

I976,B,ellar,

et

al.,

1974).

It

was soon

learned

that

these

DBPs were the

products

of the reactions of chlorine

with

the

natural

organic matter

(NOM)

present

in

the water. Following these initial

publications,

intensive research

was

conducted

to

determine

the

possible

reaction

products

of

chlorinating

potable

waters

with high

concentrations

of

naturally

occurring

dissolved

organic

matter.

Results

of

such

studies further identified numerous chlorinated DBPs

and

suspected carcinogens,

primarily

focusing

on

various

haloforms, with

the majority of

results citing elevated

levels

of

trihalomethanes

(THMs)

and

haloacetic acids

(HAAs).

The formation of DBPs, THMs and HAAs during the chlorine

disinfection

process

is

rapidly

emerging as one

of

the

key

disadvantages associated with

chlorination

for

potable

waters.

Continually

demanding

the

focus

of

water quality

scientists

and

engineers,

the

toxic

and

potentially

carcinogenic

properties

of THMs

have

undergone

intense

scrutiny throughout the last 20

years (American

Water Works Association.,

1990). The widespread occulrence

of haloform

pollutants

suggests that naturally

occurring hurnic

substrates

represent the

dominant

organic

precursor

to THM formation.

Research

has

demonstrated

that the chlorination

of

naturally occurring

fulvic

and

humic

acids have contributed

to the

formation of chloroform

(CHClg),

bromoform

(CHBr3),

brorrodichloromethane

(CHBrCl2),

and chlorodibromomethane

(CHBrClz)

(Reckhow,

et

al., 1990, Trussell and Umphres,

1978).

The corresponding bromine substituted by-

37


39/183

products

are

generally

thought to

be

produced

via

parallel

bromination

reactions.

These

reactions

would

originate

from

the interaction

between

chlorine and the

naturally

occurring

concentration

of bromide ions

present

in most waters

(Boyce

and

Hornig,

1983). This interaction is

presented

in equation

(11).

HOCI

+

Br-

-->

HOBr

+ Cl-

The exact

formation

mechanism

of

the

various

chlorine

and

bromine

THMs

are

not well understood.

The multitude of complex reactions

between

free chlorine and a

group

of organic

acids

commonly

referred

to as humic

acids make it difficult

to

single out

a

precise

formation mechanism. The

structures

of

incoming humic

materials

continually

undergo

various

modifications

which are dependent on,

yet

not limited

to, several natural

water

quality

parameters.

In

particular,

the concentration and speciation of dissolved

humic

materials

-

the available

FAC, seasonal changes in temperature and

pH.

All of

these

parameters,

as well as

the

contact

time with

chlorine, affect the rate, type

and

concentration

of DBPs

formed from

disinfection.

Efforts to understand,

model

and

predict humic material

concentrations, and

accordingly

adapt

chlorination

protocols,

are

normally

convoluted.

These models

usually do

not

provide

a

substantial

or

feasible

solution'

or

simply

are

regarded as

completely

ineffective

likely

due

to

the

rnultitude of

parameters

required and

poorly

understood relationships

(Gates,

1998). Current

publications

concerning experimental methods

to

resolve

THM formation are extensive

and

vary in applicability

and

feasibility

(Andre

and Khraisheh, 2009,

Kim

and

Kang,

2008, Liu, et

al., 2008, Iriarte-Velasco, et

al.,

2007, Rodriguez, 2007,

Adachi and

Kobayashi,

1995,

Reckhow, et a1.,1990,

Graham,

et a1.,1989).

These

methods

generally

range from efforts

to remove

THM

precursors

(through

improved

pre-chlorination

(11)

38


40/183

filtration

processes),

absorbing

THMs via

the use

of

granular

activated carbon

(GAC),

changing

disinfection

procedures (Graham,

et

al., 1989) and lastly through changing

water

sources.

It

was

originally

thought that

FAC

was

a

necessary factor in the formation

of

THMs,

however

the

observation of

THMs

forming in

the

absence of FAC

(notably

at

a

reduced

rate)

(Asano,2007)

challenged this

notion.

Asano noted that

initial

mixing may

affect

THM formation due

to

competing reactions between chlorine and ammonia, as

well

as

chlorine

and various

humic

acids. Additional information on THM

formation

has

been extensively

studied and

published

by

the United

States

Environmental

Protection

Agency

(EPA)

and Health Canada

(Federal-Provincial-Territorial

Committee on

Drinking

Water

of

the Federal-Provincial-Territorial

Committee

on Health and

the

Environment,2006

With 2009 Addendum,

1998).

Controlling

the

levels

of THM

precursor

concentrations

prior

to chlorination

is

deemed

the most direct means of resolving THM

problems.

Investigative studies

have

also

shown

that a substantial

reduction

in

THM

formation

can be achieved

by

the use

of

alternative disinfectants

such as

chlorine dioxide

(ClOz)

and ozone

(O:),

in lieu

of current

practices

of

breakpoint

pre-chlorination

or reduction

in the

pre-chlorination (Gates,

et al.,

200e).

With

the

discovery

of

potentially

toxic

DBPs

and

resulting

governrnent

regulations outlined

to

limit

maximum

acceptable

concentrations

(MAC)

of

total

trihalomethanes

(tTHMs)

in

potable

waters, scientists and engineers have

taken

a

heightened

interest

in

determining

alternative

disinfectants

which may

be suitable

as

a

replacement

to

classical

chlorination.

39


41/183

2.2 The

Alternative

Disinfectant: Chlorine Dioxide

Use

of

chlorine dioxide

in

Manitoba has

been

incredibly limited, largely due

to

the

small

knowledge

base

demographically available,

and

the lack

of

specific

yet

readily

applicable

analytical

methods available

for

treatment

facilities.

Chlorine

dioxide

possesses

superior

biocidal

capacity

when

compared

to

customary chlorine

and

chloramine

disinfectants.

To compare, the chlorine

content

is

52.60/o

(the

amount

of

chlorine in

chlorine dioxide) and undergoes a 5 valence electron change,

giving

rise

the

263%

more

powerful

disinfectant

when

comparing

"available

chlorine" content.

In

particular,

chlorine dioxide has

the ability to

selectively

oxidize

compounds

and

offers

an

alternative

to

current disinfectant

processes

such as

those

which

rely

on

chlorine,

ozone

and

chloramines. Chlorine

dioxide

is not as

popular

as other

disinfectants

(ozone,

chlorine,

chloramines,

etc.)

in North

American, though

where is has been used, it

has

been applied

when not only

the

water must

be

disinfected, but

also

when

an

improvement

in

the

water's

various organoleptic

qualities

is sought. As an example,

chlorine dioxide

would

be used

in

the oxidation

of

the

sources

manganese

content

in

order

to

mitigate

colour.

Specifically,

usage of

chlorine dioxide allows

for enhanced

control via oxidation

of

several

major taste and odour contributing compounds such

as

those

containing

iron,

manganese

and sulphur.

2.2,1Chemistry of Chlorine

Dioxide

Some

basic physical properties

of

chlorine dioxide may

become evident upon

synthesis.

Chlorine dioxide, characteristically

a

greenish

yellow

gas,

when dissolved in

water

produces

a

strong,

distinctive chlorine-like,

pungent

odour.

It is a very reactive

40


42/183

species;

at

temperatures above -40oC it is

unstable and

prone

to explosive decomposition

when concentrations

exceed |)%by volume

in air

(Gates,

1998). By

the

same reasoning,

highly

concentrated solutions

of chlorine dioxide

may

be

dangerous

if the

partial

pressure

exceeds

10.1

kPa.

Additional

chemical and

physical properties

have been

previously

published

by

Kirk et al.

(1991)

and are surmarized in Table

2.

These

parameters

are

characterize

the

uniqueness of

chlorine

dioxide

as

a molecule,

as

a

gas

stable in water,

and as

a

potable

water disinfectant.

Table

2:

Selected

properties

of

chlorine dioxide,

data adapted

(Kirlq

et

al.,

1991).

Property Value

Molecular

mass

Melting

point

Boiling

point

(At

101.3kPa)

Density of liquid:

-55'C

00c

10"c

Heat of Formation

Gibbs

Free

Energy

Entropy

Heat

of

Combustion

Dipole Moment

Molar Extinction coefficient

(25

-50"C)

UV

Absorption

Maximum

Henry

Constant

67.452

g/mol

-59.6"C

10.9'C

1.773

glml-

1.640

glnL

1.614

glml-

102.5

kJ/mol

120.5

kJ/mol

0.257

kJ/rnol

-102.5

kJ/mol

1.7835

D

1250

(moVl.)/crn

360 nm

1.0

(moVl-)/atm

Chlorine

dioxide is highly

water soluble,

yet

when

compared to

chlorine

does

not

undergo

subsequent

hydrolysis

in

water

(Kap,2e3:3.94x104>>Kcrc4zsst-L.2x10-7)

and

remains

a

gas

dissolved

in

solution

(Aieta

and Berg,

1986).

As such,

when

precautions

are

taken, evaporated

reduction

in

stored solutions

can be

rninimized.

Neutral

or acidic

41


43/183

solutions

of

chlorine

dioxide may be considered stable

for

extended

periods

of

time,

if

they are stored

in

brown

glass

jars,

in

a dark, refrigerated space with

no

headspace

(white,

1999,

Gates, 1998).

The

mechanism

of

disinfection

utilized

by

chlorine

dioxide is

based upon

the

principle

that

chlorine dioxide acts as

a very

strong oxidizer

while

maintaining

some

selectivity

towards

specific

chemical attributes. The oxidation

pathway

is via a one-

electron

transfer, thus

the

resultant self-decomposition to the chlorite ion is

generalized

as

in the following

equation

(12).

Clo2+Substrate

->

CiO2- +

Substrate'

Chlorine

dioxide does not tend to cleave carbon-carbon n-bonds, and since

no

chlorine

is added to the

molecule

this

accounts

for the

lack of halogenated

by-product

forrnation

(ie.

THMs)

when compared to

using

chlorine.

However, chlorine dioxide

is

prone

to react

with

phenolic

compounds, and

rapidly reacts with

organic sulfides

and

tertiary amines.

The result of

these

reactions is the effective destruction of a multitude of

taste and odour

causing compounds

(Gates,

et al.,

2009,

Gates,

1998,

Masschelein

and

Rice, 1979).

Reactions

with primary

and secondary amines, alcohols, and carbonyls

are

considered slow,

whereas

reaction

rates

with

aqueous chlorine,

iron(Il)

and

manganese(Il)

vary

depending

upon equilibrium conditions

(Masschelein

and Rice,

L979).

From

a chemical standpoint,

efforts to describe the

species

and

concentrations of

42

(r2)


44/183

by-products

produced

when

using

chlorine

dioxide are

not

of

a

straightforward

stoichiometric

nature. There is no single descriptor

-

whether

functional

group,

reaction,

or

general

molecule

-

to describe

all

potable

water

sources. One must consider

several

redox

couples to describe

the

nature of

the

oxidation disinfection

process.

The

primary

oxidation

half

reactions of chlorine dioxide are

presented

as

in

Table 3. Values

are

reported

at room

temperature and

standard

pressure

with

respect to a

standard

hydrogen

electrode

and

the

presented

data

has

been adapted

(Lide,

1999).

Table 3: Standard reduction

potentials

of

several

oxidation

states

of

chlorine

at25oC,

data

adapted

(Lide,

1999).

Standrd

Potential,

Equston Eo

(V)

pe

(:logK)

Oxidation No.

Reactant

Chlorine

Y,

CIO+'+

H+

+

e-

:

Yz

ClO3-

+

HzO

ClO3-

+

2H*

+e-:

ClOz

+

H2O

Y2

Cl9.-

+

H*

+

e'

:

Yz

ClOz-

+

%

HzO

ClO2luq

+

H"

+

e-: HCIOz

CIO',".'

*

e-:

ClOr-

\eY/

r/qHClOz+t/olf.*

*e-:

/+CI-

+YzHzO

HCIO

+

H*

+

e-

:

/,

Clz(uq)

+

HzO

%ClO-

+

YzHzO

*

e-:

t/zCl'+

OH'

lz

Cbruq)

-|

e-

:

Cl-1aq

20.09

7

19.47 s

s.58

5

2r.s8

4

r6.t2

4

27.80

3

26.53

3

27.23

I

13.69

1

23.59

0

lzHClOz

+

H*

+

e-

:

Yz

HC1O

+

YzHzO

1.645

1.189

r.t52

0.33

1.277

0.954

l.sl

1.61 I

0.810

r.396

The use of a Latimer diagram

is

normally

used to convey the

information

contained in Table 3 in a concise manner which

summarizes

the

standard electrode

potentials

relative

to

the element in

question,

chlorine.

Use

of

the Latimer diagram

can

also indicate

if

a species has a tendency to disproportionate in

solution

given

the

conditions

in which the electrode

potentials

in Table

3

are

presented (25"C).

Specifically,

if the

potential

displayed to the right of the

species is

higher

than the

potential

displayed

43


45/183

to the

left, the

species

can

oxidize

and reduce itself, commonly

known

as

disproportionation.

The

Latimer

diagram for

chlorine

is

presented

as Figure

4,

potentials

are

presented

in

units of

Volts

and

has

been adapted

from

Standard Potentials in Aqueous

Solution

(IUPAC)

(Bard,

et

al.,

1985).

Oxidation

States:

o

oe

tl

()

;o.

.=v

o

Oxidation

States:

o

o-

CA

II

o-c

'

o.

dv

o

+5

t.t75

+3

t.188

+1

1.6s9

1.63

HCIO

1.35828

..'CI

r.35828

cl,

cl

-1

+7

+5 +4

-0.481

0.374

clo4- Cl9r-#

ClO2-

r-

ClOz

-r

o.zos

,1,

1.468

+3 +1

1.071

0.68r

CIO-

0.42r

0.488 0.89

Figure

4:

Latimer diagram for chlorine in both acidic

and basic

solution, diagram

adapted

@ard,

et

al.,

1985).

Figure 4 effectively

describes the

thermodynamic stability

of various

oxychlorine

species.

Variations in

potentials

using

the two

different media

(ph

extremes)

are

due

to

the

involvement

of

a

proton

(H*)

or hydroxyl

group

(OH)

in the individual

standard

reduction potential

half reactions.

If

no

such

involvement is

present,

the

values remain

the

same;

as seen

in

for

the

potential

describing

the

reduction of chlorine to chloride.

Alternatively, use

of

a Frost diagram can

represent electrode

potentials

in a

diagrammatic

form. Frost

diagrams, as

in Figure

5, of

chlorine

provide

a

quick

44

l*il?; lffi

lO3

HCIO2..


46/183

qualitative

representation

as to the chemical

properties

of

several oxychlorine

species.

Qualities

which

may

be

sought from Figure

5 are

the following: the

species

with the most

positive

slope

is a

strong oxidizer, the

species which

lies

above

the

line connecting

two

adjacent

points

will

undergo disproportionation,

and two species

which lies

below

a line

joining

two terminal species will

comproportionate

into an

intermediate

species.

These

qualitative

characteristics

can

describe the unique

stability of

chlorine dioxide,

that it is a

radical,

kinetically existing

for a

prolonged

period

of

time,

yet

therrnodynamically

unstable.

Figure 5: Frost diagram

representing various

chlorine

species

in

acidic

and basic

conditions,

values

were

calculated

based on

standard

potentials,

data

adapted

(Miessler

and Tarr, 2004).

On a molecular

level, chlorine dioxide

corresponds to the oxidation number 5 of

chlorine

which

provides

for

2630/o

more

"available

chlorine". Having

an

angular

structure

with

the

presence

of an

delocalized unpaired

electron

(and

therefore

no

Frost Diagram of Chlorine

at

Extreme

pH's

and 25'Celsius

-----

Acidic,

pH

=0

--o-.Basic,

pH

=14

,r

,_-_--v

-o:'^._-

ClO2-

7

Thermodynamically most

stable

(acidc

and basic)

45


47/183

tendency

to

dimerize), it

is

considered

a

free radical

with a

resonance

structure

as

demonstrated

in Figure

6.

r.47l^

("2

*J)

--

("2

x)

v

117.5"

C2y Symmetry

Figure

6:

Free-radical monomer chlorine dioxide.

Chlorine dioxide

possesses

several

chemical

qualities

that

allow it to

be used

not

only to

improve

overall

water

quality,

but

also to be used as an efficient disinfectant.

When

considering

popular

disinfectants,

there exists

a wide

range

of

oxidation

potentials

without

a clear

trend linked to

capabilities.

For example, both ozone and hydrogen

peroxide

have

high

oxidative

potentials,

with ozone arguably being the more

popular

disinfectant.

In

comparison,

chlorine dioxide

has a

much

lower

oxidation

potential

and

yet

retains

admirable disinfection characteristics,

as

well

as

selective oxidizing

properties

(Parga,

et

a1.,2003).

Table 4:

Common

disinfectants

and

their

associated

oxidation values

at25'C.

Species

Oxidtion

Potential

E"

(Volts)

Half

Rection

Ozone

2.706

Hydrogen

peroxide

1.776

Potassium

permangan ate |

.61

9

Hypochlorousacid

1.482

YzOt+H*+e-:lr}z+%HzO

lzIF-.zOz+

H*

+

e-: HzO

'/,

Mnoo-

+alt:H* *

e-:

'lr}y'rnor+2l3w2o

t/rHClO

+

YrH*

f

e-:

%Cl-

+

%HzO

t/zCl26

+

e-:

Cf

ClO2luq

*

e-:

ClO2-

%CIO-

*

e-*

lrHzO:lrCF

+

OH-

Chlorine

Chlorine

dioxide

Hypochlorite ion

1.358

0.954

0.81

*Bold

face

indicates common

use

as

disinfectant

46


48/183

The

chlorine_dioxide as water disinfectant

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